When the system is full of coolant, you will need to bleed air out of it. This applied only to the cars that have the expansion tank attached to the side of the radiator. Other BMWs with a separate, external expansion tank are self-bleeding. The procedure for bleeding these cars seems somewhat sloppy and not too slick. With the bleed screw removed, fill the expansion tank until fluid begins coming out of the bleed screw. Continue filling until there are no more bubbles coming out, as shown in Figure 13. This, of course will mean that plenty of coolant will spill all over your radiator, and down onto the ground. Have a catch pan ready to capture this coolant spill. When no more bubbles exit out of the bleed screw, tighten it to 8 Nm (71 in-lb).
Now, run the engine until it reaches it's operating temperature. Turn off the engine and let it cool down. Then, top off the coolant in the expansion tank to the appropriate level, if necessary.
Som redan nämnts så är det jättevanligt på M50 motorn att skovelhjulen släpper. Om/när du byter, se till att köpa en vattenpump med skovelhjul i metall, INTE i plast som orginalet har.